1. Field of the Invention
The present invention relates to a light guide sheet and a movable contact element using the sheet, which are used to operate various electronic apparatuses.
2. Background Art
In recent years, an increasing number of electronic apparatuses such as portable telephones and other portable terminals have come to use light emitting diodes or EL (electroluminescent) devices as light sources to illuminate their operating parts. The illumination allows the user to easily distinguish between push buttons or to operate the display in dark environments. In line with this trend, light guide sheets, movable contact elements, and switches which are used in these apparatuses are also expected to be less expensive and capable of being illuminated in such a manner as to provide the user with better visibility.
FIG. 7 is a sectional view of a conventional switch. In FIG. 7, the dimensions of some parts are exaggerated for clarity.
The switch includes movable contact element 3 having film-like base sheet 1 and dome-shaped movable contacts 2 pasted on its bottom surface via an adhesive (not shown). Movable contacts 2 are formed of a conductive sheet metal. The switch also includes wiring board 4, which is provided on its upper and lower surfaces with wiring patterns (not shown). Wiring board 4 is also provided on its upper surface with fixed contacts 5 each consisting of circular central fixed contact 5A and horseshoe- or ring-shaped outer fixed contact 5B surrounding central fixed contact 5A.
Movable contact element 3 is pasted on the upper surface of wiring board 4 in such a manner that the outer peripheries of movable contacts 2 are placed on outer fixed contact 5B and that the centers of the bottom surfaces of movable contacts 2 are opposed to central fixed contacts 5A with a predetermined spacing therebetween. The switch also includes light-emitting devices 6 composed, for example, of light emitting diodes, which are arranged between movable contacts 2 on the upper surface of wiring board 4 with their light emitting surfaces facing upward.
The switch also includes light-transmissive, film-like display sheet 7, which is provided on its bottom surface with light shielding part 7A and display parts 7B. Light shielding part 7A is formed by printing or other means, and display parts 7B are formed by hollowing predetermined positions of light shielding part 7A out in the shape of characters, symbols, and other graphic elements. Display parts 7B are arranged over movable contacts 2.
The conventional switch thus structured is installed on the control surface of an electronic apparatus, with central fixed contacts 5A, outer fixed contacts 5B, and light-emitting devices 6 connected to electronic circuits (not shown) of the apparatus via the wiring patterns, lead wires (not shown), and the like.
When the user presses one of display parts 7B of display sheet 7, display sheet 7 is bent to press the dome-shaped center of movable contact 2 that corresponds to the pressed display part 7B. When a predetermined compressive force is applied, movable contact 2 is elastically inverted downward with a click feel. As a result, movable contact 2 comes into contact at the center of its bottom surface with central fixed contact 5A, thereby electrically connecting central fixed contact 5A and outer fixed contact 5B. This allows an electronic circuit of the apparatus to detect which one of display parts 7B has been pressed.
When the user releases the compressive force applied to display sheet 7, movable contact 2 is elastically inverted upward by the elastic returning force. As a result, the center of the bottom surface of movable contact 2 is separated from central fixed contact 5A, thereby electrically disconnecting central fixed contact 5A and outer fixed contact 5B.
The electrical connection and disconnection switches the functions of the apparatus. When power is supplied from an electronic circuit of the apparatus, light-emitting devices 6 emit light, which illuminates display parts 7B of display sheet 7 from below. This allows the user to easily distinguish between the characters, symbols, and other graphic elements on display parts 7B in dark environments.
As described above, in the conventional switch, fixed contacts 5A and 5B are electrically connected and disconnected by pressing and releasing movable contacts 2 via display sheet 7, and display parts 7B of display sheet 7 are illuminated by the light emitted by light-emitting devices 6. A conventional technique related to the present invention is disclosed in Japanese Patent Unexamined Publication No. 2007-87749.
In movable contact element 3 and the switch of the above-described conventional example, light-emitting devices 6 are arranged between movable contacts 2 and illuminate display parts 7B of display sheet 7. This structure requires a large number of light-emitting devices 6, thus taking time for production and being expensive.